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Upgrade from Honeywell IAQ 9000 to Nest

So, subject says the gist. I'm curious if this is even a feasible upgrade, and whether or not it would even be worth it.

Has anyone seen a system go this way? I bought the IAQ largely because it was the best you could really get at the time (2008) to control my HP and AH.

Heck, I don't even know if the Nest is capable of controlling everything fully.

Anyone know?

HP and AH are both Trane.

XL15i, 4TWX5030B1 with the 4TEE3F39A1 air handler.

I would imagine an installer would need to remove the back end of the IAQ, and wire the Nest directly into the AH (since I'm pretty sure between the backend unit, and the thermostat, there are only 3 active wires).

By "worth it", I guess I meant, would I lose some key function of the IAQ? I didn't mean, "Would this pay for itself". I'm a geek, it doesn't need to if it's cool enough, or has some killer feature (like, being able to access it online).

So I'd assume, given the response, you haven't done this "upgrade" yourself, or seen a case of it done. So whether the nest will handle everything the IAQ does, is unknown.

Basically, I'd imagine it must be able to talk to the external thermistor so it knows where the balance point of the HP is. And I'd assume that one could set that balance point manually. That it should be able to handle the variable speed AH fan (runs all the time at low speed, ramps up when there's heating/cooling). What about using the AC for dehumidifying? I guess I'm unsure of what functionality is controlled internally by the HP and AH, and what is controlled by the IAQ.

I guess really I'm looking for input from an HVAC tech that's actually worked with a Nest before in a HP setting, since the Nest site doesn't have a lot of the technical details (that I can find). Guess they're like Apple in that way as well.

I've installed a few nests, two on heat pumps. As far as the coolness factor goes I'd give it a thumbs up, but it's not all that "smart" a thermostat when it comes to HVAC technology. It's really just a basic thermostat that has wifi capabilities and an app for your phone so it can be accessed remotely. No real user configurable settings.

The Nest thermostat doesn't do dehumidification, or work with outdoor temperature sensors, so you would lose a couple of key capabilities of the IAQ thermostat.

Depending on where the thermostat is located, the "learning" function of the Nest thermostat will be completely useless. The occupancy sensor needs line of sight to people moving around for that feature to work.

The "cool factor" of having control of the thermostat from your phone, or computer, wears off pretty quickly. For the vast majority of people, it is completely pointless.
For me personally, the "cool factor" wore off after about a month.
The only thing I use the internet control capabilities of my Ecobee thermostat for is remote monitoring of a small home built chiller system I use for a water cooled computer system. The Ecobee thermostat has an add on sensor board that a number of remote sensors can be tied into, and sets of dry contacts that can be used to turn things on and off. It also has some configurable alert options I find useful.
The Nest thermostat has none of those capabilities.

Thanks Mark! So, I'm curious, how does the Nest know when to use emergency/secondary heat if it doesn't work with an outdoor temp probe?

But heck, you answered a follow up question as well, which is "what about the Ecobee".

At this point, I'm probably going to stick with the IAQ since it does "just work". Sure, it's kinda ugly, but it gets the job done.

And the dehumidification thing, I'm sure they could add via software update (since all the system does is run the AC for a bit before ramping up the fan so the evap coils are nice and cold, then pull all that moisture out of the air with that). Seems like a software update could add that feature pretty easily.

Thanks Mark! So, I'm curious, how does the Nest know when to use emergency/secondary heat if it doesn't work with an outdoor temp probe?

But heck, you answered a follow up question as well, which is "what about the Ecobee".

At this point, I'm probably going to stick with the IAQ since it does "just work". Sure, it's kinda ugly, but it gets the job done.

And the dehumidification thing, I'm sure they could add via software update (since all the system does is run the AC for a bit before ramping up the fan so the evap coils are nice and cold, then pull all that moisture out of the air with that). Seems like a software update could add that feature pretty easily.

Thanks again!

The IAQ when wired up correctly and set correctly, will keep the blower slowed until the humidity is back down to set point, or until the cooling call and cool to dehumidify call is over. Not just on start up.

Maybe, but got you to give meaningful detail to your original question.

:-)

Originally Posted by staze

Thanks Mark! So, I'm curious, how does the Nest know when to use emergency/secondary heat if it doesn't work with an outdoor temp probe?

2 stages of heat, one of cooling. I believe backup would be second stage. They have a pretty thorough q/a and blog on their site. If you have better equipment, this is a very pretty turd.

Communicating equipment does A LOT MORE than just delay the fan. I'm not sure how much of those features translate down to iaq, but I suspect you are underestimating what that unit does. (oop, bt jumped in with the answer above - that's a BIG feature).

I greatly dislike the Nest, the technology is not HVAC technology. Stick with the Honeywell Prestige 2.0 with redlink kit for the best control. I am constantly seeing those horrible Nest thermostats because of their flashy look the Nest would be a downgrade for you.